ubuntu-cve-2026-55199
Vulnerability from osv_ubuntu
Published
2026-06-17 20:17
Modified
2026-06-30 16:23
Summary
Details
libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set nr_extensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over 60 seconds because return values from _libssh2_get_string() are unchecked and the session timeout does not apply to CPU-bound loops.
Severity
5.9 (Medium)
7.5 (High)
N/A (UNKNOWN)
References
{
"affected": [
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libssh2-1",
"binary_version": "1.4.3-2ubuntu0.2+esm3"
}
]
},
"package": {
"ecosystem": "Ubuntu:Pro:14.04:LTS",
"name": "libssh2",
"purl": "pkg:deb/ubuntu/libssh2@1.4.3-2ubuntu0.2+esm3?arch=source\u0026distro=esm-infra-legacy/trusty"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.4.3-1",
"1.4.3-2",
"1.4.3-2ubuntu0.1",
"1.4.3-2ubuntu0.2",
"1.4.3-2ubuntu0.2+esm1",
"1.4.3-2ubuntu0.2+esm2",
"1.4.3-2ubuntu0.2+esm3"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libssh2-1",
"binary_version": "1.5.0-2ubuntu0.1+esm2"
}
]
},
"package": {
"ecosystem": "Ubuntu:Pro:16.04:LTS",
"name": "libssh2",
"purl": "pkg:deb/ubuntu/libssh2@1.5.0-2ubuntu0.1+esm2?arch=source\u0026distro=esm-apps/xenial"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.5.0-2",
"1.5.0-2ubuntu0.1",
"1.5.0-2ubuntu0.1+esm1",
"1.5.0-2ubuntu0.1+esm2"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libssh2-1",
"binary_version": "1.8.0-1ubuntu0.1"
}
]
},
"package": {
"ecosystem": "Ubuntu:18.04:LTS",
"name": "libssh2",
"purl": "pkg:deb/ubuntu/libssh2@1.8.0-1ubuntu0.1?arch=source\u0026distro=bionic"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.8.0-1",
"1.8.0-1ubuntu0.1"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libssh2-1",
"binary_version": "1.8.0-2.1ubuntu0.1"
}
]
},
"package": {
"ecosystem": "Ubuntu:20.04:LTS",
"name": "libssh2",
"purl": "pkg:deb/ubuntu/libssh2@1.8.0-2.1ubuntu0.1?arch=source\u0026distro=focal"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.8.0-2.1build1",
"1.8.0-2.1ubuntu0.1"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libssh2-1",
"binary_version": "1.10.0-3"
}
]
},
"package": {
"ecosystem": "Ubuntu:22.04:LTS",
"name": "libssh2",
"purl": "pkg:deb/ubuntu/libssh2@1.10.0-3?arch=source\u0026distro=jammy"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.9.0-3",
"1.10.0-2",
"1.10.0-2build1",
"1.10.0-3"
]
},
{
"ecosystem_specific": {
"availability": "No subscription required",
"binaries": [
{
"binary_name": "libssh2-1t64",
"binary_version": "1.11.0-4.1ubuntu0.24.04.2"
}
]
},
"package": {
"ecosystem": "Ubuntu:24.04:LTS",
"name": "libssh2",
"purl": "pkg:deb/ubuntu/libssh2@1.11.0-4.1ubuntu0.24.04.2?arch=source\u0026distro=noble"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.11.0-4.1ubuntu0.24.04.2"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.11.0-2",
"1.11.0-3",
"1.11.0-4",
"1.11.0-4.1build1",
"1.11.0-4.1build2",
"1.11.0-4.1ubuntu0.24.04.1"
]
},
{
"ecosystem_specific": {
"availability": "No subscription required",
"binaries": [
{
"binary_name": "libssh2-1t64",
"binary_version": "1.11.1-1ubuntu0.25.10.2"
}
]
},
"package": {
"ecosystem": "Ubuntu:25.10",
"name": "libssh2",
"purl": "pkg:deb/ubuntu/libssh2@1.11.1-1ubuntu0.25.10.2?arch=source\u0026distro=questing"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.11.1-1ubuntu0.25.10.2"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.11.1-1",
"1.11.1-1build1",
"1.11.1-1ubuntu0.25.10.1"
]
},
{
"ecosystem_specific": {
"availability": "No subscription required",
"binaries": [
{
"binary_name": "libssh2-1t64",
"binary_version": "1.11.1-1ubuntu0.26.04.2"
}
]
},
"package": {
"ecosystem": "Ubuntu:26.04:LTS",
"name": "libssh2",
"purl": "pkg:deb/ubuntu/libssh2@1.11.1-1ubuntu0.26.04.2?arch=source\u0026distro=resolute"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.11.1-1ubuntu0.26.04.2"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"1.11.1-1build1",
"1.11.1-1build2",
"1.11.1-1ubuntu0.26.04.1"
]
}
],
"aliases": [],
"details": "libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set nr_extensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over 60 seconds because return values from _libssh2_get_string() are unchecked and the session timeout does not apply to CPU-bound loops.",
"id": "UBUNTU-CVE-2026-55199",
"modified": "2026-06-30T16:23:41Z",
"published": "2026-06-17T20:17:00Z",
"references": [
{
"type": "REPORT",
"url": "https://ubuntu.com/security/CVE-2026-55199"
},
{
"type": "REPORT",
"url": "https://www.cve.org/CVERecord?id=CVE-2026-55199"
},
{
"type": "REPORT",
"url": "https://github.com/libssh2/libssh2/pull/1864"
},
{
"type": "ADVISORY",
"url": "https://ubuntu.com/security/notices/USN-8486-1"
}
],
"related": [
"USN-8486-1"
],
"schema_version": "1.7.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
},
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
},
{
"score": "medium",
"type": "Ubuntu"
}
],
"upstream": [
"CVE-2026-55199"
]
}
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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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